The use of atomic absorption spectrometers to perform chemical analysis based on the absorption or attenuation by matter of electromagnetic radiation of a specific wavelength is well known. An analysis of the spectrum of light passed through a sample provides information regarding the composition of the sample. In one type of spectrometer, a concave grating is used to focus the spectrum on a circular circumference known as the Rowland circle. The use of Rowland circles in spectrometry is well known. Although the use of a concave grating to focus spectrum along the Rowland circle is advantageous, the geometries required have been difficult to obtain and adjust for optimum performance. Independent adjustments for shifting the spectrum along the Rowland circle and focussing it thereon are not possible with prior art devices. The use of photomultiplier tubes to detect the spectrum lines along the Rowland circle is also well known. Typically, the photomultiplier tubes would be spaced along the Rowland circle at predetermined locations to detect specific spectrum lines characteristic of a specific element attempting to be identified. While this direct reading method was acceptable in many instances, difficulties were encountered when multiple elements needed to be detected in a single sample and the spectrum to be detected was physically closer than the photomultiplier tubes were able to be positioned.